In the field of advanced semiconductor manufacturing, it is well known to expose a semiconductor sample, such as a semiconductor wafer containing blanket metal or insulating films and a photoresist exposed with patterns to a reactive ion etching (RIE) process using a mixture of gases containing but not limited to chlorine and/or fluorine. The purpose of such an etching process is to define patterns in the films. The photoresist is then typically stripped in an oxygen plasma. The remaining residues often need to be removed by chemicals and/or solvents in order to achieve high yield.
For example, Al metal etching is the most commonly used to define wiring on the semiconductor wafers. Despite cleaning and rinsing the semiconductor wafer, unwanted residue still remains on the top and the sidewalls of the metal lines. This unwanted residue, which remains on the top and sidewalls of the metal lines, reportedly includes the elements carbon, hydrogen, silicon, aluminum, fluorine, chlorine and oxygen. Such residue, which is referred to herein as RIE residue, is known to be conductive enough to cause shorts between metal lines. Moreover, the RIE residue may also cause adhesion problems between the metal lines and the overlying insulator. The RIE residue on metal lines may cause corrosion of the semiconductor sample. The RIE residue on polysilicon lines or oxide vias also cause yield loss problems. Thus, there is considerable interest in the field of advanced semiconductor manufacturing for developing a chemically safe and easy method for removing the RIE residue from a semiconductor sample.
The current method which is typically being used for removal of this unwanted RIE residue in advanced semiconductor manufacturing processes involves soaking the etched semiconductor sample in an acid bath.
These and other objectives are met by the present method which uses a supercritical fluid or liquid CO.sub.2 as solvents for removing the residue from a precision surface which has been first subjected to an etching process.
It is emphasized that supercritical fluids, such as supercritical fluid CO.sub.2, are, however, currently being used in semiconductor processing for developing a resist pattern layer on a substrate. Such a process is disclosed, for example, in U.S. Pat. No. 4,944,837 to Nishikawa et al. Specifically, Nishikawa et al. provides a method of forming a patterned resist film having a predetermined pattern on a surface layer formed on a substrate comprising the steps of depositing a resist film on the surface layer, pre-processing the resist film into a pre-processed resist film which is attached to the surface layer and which has a latent image of the predetermined pattern, and processing the pre-processed resist film into the patterned resist film. In accordance with the disclosure of Nishikawa et al., the processing step comprises introducing the pre-processed resist film together with the substrate into a supercritical atmosphere and developing the pre-processed film in a supercritical atmosphere to selectively remove the pre-processed film.
Other examples of using supercritical fluids in semiconductor manufacturing are disclosed in U.S. Pat. Nos. 5,185,296 and 5,304,515, both to Morita et al. In both of these disclosures, supercritical fluids are used for forming a dielectric thin film or pattern thereof on the surface of a semiconductor substrate. As in the above reference to Nishikawa et al., the supercritical fluids are used in both of the Morita et al. references to develop the pattern resist film on the surface of the semiconductor substrate.
In an article by ziger et al. entitled "Compressed Fluid Technology: Application to RIE-Developed Resists", AICHE Journal, Vol. 33, No. 10, October 1978, compressed CO.sub.2 i.e., supercritical fluid CO.sub.2, is utilized in the area of microlithography to extract nonvolatile siloxane molecules from a host organic polymer.
Despite the use of supercritical fluids in the prior art there is no known disclosure of using a supercritical fluid to remove residue from a precision surface such as a semiconductor sample which contains such residue thereon.